A Novel Reflective Surface for an UHF Spiral Antenna

As is well known, metallic cavity backings reduce antenna gain particularly for broadband configurations at low frequencies. This letter presents a novel reflective surface consisting of a ferrite tile with variable conductive coating as a backing for a conformal UHF spiral antenna. The ferrite material is used in the outer region to preserve the free-space antenna gain at low frequencies. Toward the center, the backing tapers to a conductive coating making it suitable for high frequency operation. It is shown that this hybrid surface (ferrite to metallic) improves the antenna performance significantly at lower frequencies without compromising the high frequency gain.